STAT (signal transducers and activators of transcription), a transcriptional regulator, is a DNA-binding protein whose activity is regulated by stimulations of various cytokines (IL-6, interferon, etc.) or growth factors (EGF, PDGF, etc.). Upon binding of cytokines to their receptors, JAK (Janus protein tyrosine kinase) kinase is activated to phosphorylate tyrosine in STAT (see e.g., Non Patent Documents 1 and 2). Moreover, upon binding of growth factors to their receptors, tyrosine kinase possessed by the growth factor receptors themselves phosphorylates STAT (see e.g., Non Patent Document 3). The phosphorylated STAT is activated by dimerization via its Src homology 2 (SH2) domain. The activated STAT moves into the nucleus where it specifically recognizes and binds particular DNA sequences in the gene promoter regions to induce the transcriptions of many genes. Specifically, STAT is a mediator essential for signal transduction pathways from cell surface to the nucleus and is deeply involved in cell growth or differentiation, etc.
For STAT, 6 different members (STAT1, STAT2, STAT3, STAT4, STAT5, and STAT6) and some isoforms (STAT1α, STAT1β, STAT3α, and STAT3β) are known.
Of them, STAT3 is expressed in the majority of cytomas (see e.g., Non Patent Document 4). Its constitutive activation and overexpression are observed in various cancer cells such as breast cancer, lung cancer, prostatic cancer, head and neck cancer, skin cancer, pancreatic cancer, and ovarian cancer cells, and in cancer cells such as myeloma, breast cancer, prostatic cancer, brain tumor, head and neck cancer, melanoma, leukemia lymphoma, and multiple myeloma cells (see e.g., Non Patent Documents 5, 6, and 7). The growth or invasion of these cancer cells is considered to depend on STAT3. Moreover, the abnormal or constitutive expression of STAT3 is also involved in cellular transformation (see e.g., Non Patent Documents 8, 9, and 10). Thus, STAT3 is probably useful as a target molecule for these cancer types. Its inhibitor is therefore expected as an anticancer agent.
It has been reported that an antisense oligonucleotide complementary to the translation initiation region of STAT3 actually inhibits TGF-α-stimulated cell growth induced by an epidermal growth factor receptor (EGFR) (see e.g., Non Patent Document 11). It has also been reported that inhibition of STAT3 functions (using antisense, RNAi, peptides, or the like) can suppress the growth of cancer cells and induce apoptosis. This suggests that a STAT3 inhibitor can serve as a therapeutic or preventive drug for cancer.
For example, 6-nitrobenzo[b]thiophene-1,1-dioxide (see e.g., Non Patent Document 12) and a phosphorylated oligopeptide (see e.g., Non Patent Document 13) are known as compounds inhibiting STAT3.
A 3-aminopyrazole derivative represented by the following formula (A):
(wherein R represents an alkyl group, a cycloalkyl group, or the like, and R1 represents an alkyl group, a heterocyclic group, an aryl group, or the like) [0010] is known as a therapeutic drug for cancer and cell proliferative disorder (see e.g., Patent Document 1). Examples of the aryl group include a phenyl group as well as aromatic heterocyclic groups such as pyridyl and quinolyl.
Moreover, a quinoline derivative represented by, for example, the following formula (B):
is known to have caspase inhibitory activity (see e.g., Patent Document 2).
Furthermore, a (thiadiazolyl)quinolinecarboxamide derivative represented by, for example, the following formula (C):
is known to have antimicrobial or antifungal effect (see e.g., Non Patent Document 14).